European Patent Application No. 713 005 describes how a connecting means for connecting an ignition coil to a spark plug is manufactured through the use of a spark plug connector, an ignition cable, and a spark plug connector. Before the manufacture of the connecting means, these components of the connecting means were separate structural members having their own closing element as casing or covering cap.
This covering cap, for the most part made of a special rubber mixture, is particularly at risk in internal combustion engines of today. Contributing in particular to the stressful conditions is the fact that there is engine encapsulation in today's engines, as a result of which the covering cap undergoes high thermal stress.
Furthermore, deep spark plug recesses that are sealed with recess sealing are implemented in four-valve engines. As a result, a corrosive atmosphere that corrodes the covering cap can build up in the spark plug recess due to lack of air exchange.
Finally, long spark plug lives are prescribed nowadays. In order to still be able to guarantee the full operativeness of the ignition system even at the end of the useful life, there is a tendency towards higher ignition voltages that endanger the electric insulation property of the covering cap through discharge voltages. These discharge voltages or partial discharges occur from the surface of the covering cap to the electrically grounded cylinder head of the internal combustion engine if there are electrically insulating air inclusions or an air gap between the surface of the covering cap and the surface with ground potential.
The aforementioned factors may, individually or in combination, result in a brittleness of the covering cap, and, consequently, to a failure of the connecting means. Since the partial discharges have the greatest influence on the brittleness of the covering cap here, this type of damage should be avoided, in particular.